One of the major defence mechanisms of animals against pathogenic organisms consists of the presence of antibodies in the tissues and fluids of the animal. These antibodies are proteins, normally referred to as immunoglobulins or gammaglobulins, which react specifically with antigens such as pathogenic organisms and their metabolic products.
An animal such as a piglet is born lacking antibodies. It receives its protection by ingesting colostrum, (which contains appreciable quantities of antibodies), normally from the mother. These colostral antibodies represent the animal's protection against disease until it develops its own antibody generating system, which in piglets does not normally start until the animal is at least ten days old. Until the animal is a few days old and has ingested significant amounts of antibodies e.g. from colostrum, the animal has little or no defense against invading pathogenic organisms.
In the case of piglets, it frequently occurs in normal farm practice that newborn piglets do not receive any or sufficient immunoglobulins. Swine litters tend to be large, often larger than the sow can nurse. Off-spring of agalactic sows will receive no colostrum from the mother. Also of course, the sow may die during farrowing. In all such cases, the piglet is extremely vulnerable to contracting infectious disease, especially scours. Pig scours are a major factor in the heavy losses of piglets in the period between birth and weaning (about six weeks old), which losses are estimated to be as high as 20% of all newborn piglets.
In addition, attempts are being made to improve the economics of raising pigs, by reducing or eliminating the weaning period. Such a zero-weaning operation can substantially increase the number of offspring per year which a sow can produce. In all such cases, however, it is necessary to provide the piglets with an alternative source of immunoglobulins during the first few days after birth.